Practitioners of medicine or surgery frequently advise a patient to undergo an invasive procedure for either diagnostic or therapeutic reasons. One such invasive procedure involves the use of a trocar which is a sharpened cannula or cylindrical instrument for piercing the wall of a body cavity to minimize traumatization to the tissue through which the endoscopic instrument is passed and to stabilize such endoscopic instrument as well as to provide a seal for insufflation of gasses to expand the operating theater. Thus, the practitioner can gain access to the cavity to withdraw a substance such as a fluid or biopsy specimen, to introduce a gas such as carbon dioxide or an instrument, such as a surgical tool. A laparoscope, a flexible fiberoptic endoscope, is an example of a surgical instrument often introduced through a trocar. The trocar barrel also helps to avoid trauma to the tissue surrounding the opening while inserting and withdrawing a surgical instrument.
Any of the numerous body cavities can be accessible to trocar invasion. Sites for introduction of a trocar include the abdomen and the pelvis. A laparoscope can be introduced through the trocar for visualization, biopsy, and certain surgical procedures. Other body cavities which commonly benefit from endoscopic procedure include the thoracic, cranial, and various joint cavities.
A general technique for introduction of a trocar includes induction of appropriate anesthesia which may be general, local or a combination of both. The area to be pierced by the trocar, such as the skin of the abdomen, is prepped and cleansed conventionally. Typically, the operator makes a nick or a small skin incision with a scalpel blade. The sharpened tip of the conventional trocar is introduced through the nick or incision, and the conventional trocar is pushed downward to and through the fatty tissue. The conventional trocar is further pushed so that its sharpened tip pierces the muscular fascial layer to enter the abdominal cavity.
In the case of laparoscopic surgery (surgery inferior to the diaphragm) a biocompatible gas such as carbon dioxide (CO.sub.2) is introduced under pressure into the abdominal cavity to create a space between the muscular fascial layer of the inner abdominal wall and the vital organs posterior to this wall. Such vital organs in the abdomen include the bowel (large and small intestine), the liver, stomach and other structures. Use of CO.sub.2 insufflation of the pelvic region tends to protect the bladder and the reproductive organs as well as their associated vascular structures from inadvertent puncture by the sharpened trocar. This is so because of the increased separation between the organs resulting from the expansion of the abdominal cavity due to internal CO.sub.2 gas pressure.
A problem attendant to using a sharp tipped trocar in body cavities is the possibility of accidentally piercing or disturbing tissue not intended to be violated. Typically, such tissue is deep to the wall covering the cavity. For example, puncture of the bowel is a complication of trocar use in the abdominal cavity. Complications from inadvertent puncture with the trocar can range from minor to serious. For instance, nicking the uterus with a trocar during a pelvic laparoscopy may be a minor event requiring no therapeutic reaction. Nicking an artery such as the ovarian artery, however, would require immediate surgical repair. Repair may not be possible through a laparoscope but may instead require an open procedure. Similarly, accidental nicking of the intestine could require immediate surgical repair.
Even if repair is undertaken aggressively, complications may ensue. For example, loss of blood from a severed artery could require a transfusion and could result in morbidity or mortality. Similarly, a pierced bowel, although promptly treated, may result in abdominal complications including peritonitis which is an acute inflammatory condition. Other complications can include abdominal infection which, if it goes undetected, can result in abscess formation or subsequent peritonitis. These conditions can be fatal.
The inadvertent puncture of a structure while placing a sharpened trocar can occur in part because the operator is pushing against the abdominal wall inwardly as the trocar is introduced. This action tends to decrease the space between the internal aspect of the abdominal wall and vital structures such as the bowel. In any event, the essential problem is that the trocar is advanced too deeply through and beyond the abdominal facial and cuts into a vital structure accidentally.
One approach to help solve this problem has been the use of auto sheathing. Auto sheathing means that the trocar device includes a means for detecting absence of resistance. When this absence of resistance is encountered, the automatic sheathing device is activated and moves axially to cover or protect the sharpened trocar tip. Typically, this decrease or absence of resistance occurs after puncture of the inner fascial layer and as the trocar tip enters the cavity such as the abdominal cavity which offers minimal or essentially no resistance. Because a vital structure may be very close to the trocar tip shortly after the trocar tip is admitted to the cavity, the time frame for automatic sheathing to act is very narrow.
An additional complication of using the conventional trocar is that the sharpened tip causes a puncturing or incisional pattern in the shape of a Y or other nonlinear pattern. This pattern is not under the control of the operator, but rather is a feature of the device itself. Such a jagged incision tends to heal less rapidly than a simple linear incision. Additionally, in certain tissues such as muscle, a linear incision parallel to the tissue fiber planes permits more rapid healing. In contrast, a cut across the grain of the muscle fiber can prolong the healing process as well as weaken the muscle permanently due to increased formation of granular tissue.